Wireless communications with efficient channel coding

ABSTRACT

A data encoding algorithm can be used ( 120 ) to generate overhead bits from original data bits, and the original data bits and overhead bits can be transmitted in respectively separate transmissions ( 121, 123 ), if the overhead bits are needed. At the receiver, the original data bits can be determined ( 125 ) from the received overhead bits, or the received data bits and the received overhead bits can be combined and decoded together ( 126 ) to produce the original data bits.

[0001] This application claims the priority under 35 U.S.C. 119(e)(1) ofthe following copending U.S. provisional applications: 60/210,851 filedon Jun. 9, 2000; No. 60/215,953 filed on Jul. 5, 2000; No. 60/216,29060/216,436, 60/216,291, 60/216,292, 60/216,413 and 60/216,433 filed onJul. 6, 2000; No. 60/217,269, 60/217,272 and 60/217,277 filed on Jul.11, 2000; and No. 60/228,860 filed on Aug. 29, 2000. All of theaforementioned provisional applications are hereby incorporated hereinby reference.

[0002] This application is related to the following copendingapplications filed contemporaneously herewith by the inventors of thepresent application: Docket Nos. TI-31285 and TI-31286 respectivelyentitled “Wireless Communications with Frequency Band Selection” and“Wireless Communications with Efficient Retransmission Operation”.

FIELD OF THE INVENTION

[0003] The invention relates generally to wireless communications and,more particularly, to wireless communications that utilize: channelcoding; multiple data rates; multiple modulation and channel codingschemes; or automatic repeat request (ARQ).

BACKGROUND OF THE INVENTION

[0004] The IEEE 802.15 Task Group 3 has outlined requirements for a highrate wireless personal area network (WPAN). Various data rates are to beprovided to support, for example, audio, video, and computer graphics.

[0005] The present invention provides for a WPAN that supports datarates for a variety of applications including audio, video and computergraphics. According to the invention, a probe, listen and selecttechnique can be used advantageously to select from an availablefrequency spectrum a frequency band whose communication quality issuitable for communication at a desired data rate. Probe packets aretransmitted on different frequencies during a known period of time, andfrequency channel quality information is obtained from the probepackets. This quality information is used to select a desirablefrequency band. The communication quality of the selected band can alsobe used as a basis for selecting from among a plurality of modulationand coding combinations that are available for use in communicationoperations. Further according to the invention, ARQ operations can beimplemented by sending a plurality of data packets in a superpacket, andresponding with an ARQ acknowledgement packet that indicates whichpackets of the superpacket require retransmission. Further according tothe invention, a data encoding algorithm can be used to generateredundant (overhead) bits from original data bits, and the data bits andredundant bits can be sent in respectively separate transmissions, ifthe redundant bits are needed. At the receiver, the original data bitscan be determined from the received redundant bits, or the received databits and the received redundant bits can be combined and decodedtogether to produce the original data bits.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 illustrates in tabular format exemplary parameters of aWPAN according to the invention.

[0007]FIG. 2 diagrammatically illustrates exemplary configurations ofWPAN transceiver devices according to the invention.

[0008]FIG. 3 illustrates in tabular format exemplary parametersassociated with first and second operational modes of a WPAN transceiveraccording to the invention.

[0009]FIG. 4 illustrates in tabular format a transmit spectrum maskassociated with the operational modes illustrated in FIG. 3.

[0010]FIG. 5 is a state transition diagram which illustrates exemplarytransitioning of transceiver devices between the modes of operationillustrated in FIG. 3.

[0011]FIG. 6 diagrammatically illustrates an exemplary frame formatstructure for mode 2 to transmissions according to the invention.

[0012]FIG. 6A graphically illustrates exemplary constellation points ofthe 16 QAM constellation which can be utilized for selected symboltransmission in mode 2 according to the invention.

[0013]FIG. 7 diagrammatically illustrates operations of an exemplaryWPAN according to the invention.

[0014]FIG. 8 is an exemplary timing diagram for communications in theWPAN of FIG. 7.

[0015]FIG. 9 diagrammatically illustrates an exemplary acquisition andpacket reception algorithms for a mode 2 receiver according to theinvention.

[0016]FIG. 10 diagrammatically illustrates an exemplary embodiment of amode 2 receiver which can implement the algorithms of FIG. 9.

[0017]FIG. 11 diagrammatically illustrates an exemplary embodiment of amode 2 transmitter according to the invention.

[0018]FIG. 12 illustrates exemplary transmit encoding and receivedecoding operations according to the invention.

[0019]FIG. 12A diagrammatically illustrates pertinent portions of anexemplary transceiver embodiment that can perform receive operationsshown in FIG. 12.

[0020]FIG. 12B diagrammatically illustrates pertinent portions of anexemplary transceiver embodiment that can perform transmit operationsshown in FIG. 12.

[0021]FIG. 13 graphically compares exemplary simulation results obtainedusing conventional Bluetooth operation (131) with exemplary simulationresults obtained using mode 2 operation according to the invention with16 QAM (132) and 64 QAM (133).

[0022]FIGS. 14 and 14A illustrate in tabular format exemplary parametersassociated with WPAN transceivers operating in mode 3 according to theinvention.

[0023]FIG. 14B illustrates part of an exemplary embodiment of the modecontroller of FIG. 19A.

[0024]FIG. 15 illustrates in tabular format a transmit spectrum maskwhich can be used by mode 3 transceivers according to the invention.

[0025]FIG. 16 graphically compares mode 3 performance with and withoutPLS according to the invention.

[0026]FIG. 17 is a state transition diagram which illustrates exemplarytransitions of transceiver devices between mode 1 and mode 3 accordingto the invention.

[0027]FIG. 18 diagrammatically illustrates operations of an exemplaryWPAN according to the invention.

[0028]FIG. 19 is a timing diagram which illustrates the exemplary statetransitions of FIG. 17 and exemplary operations which can be performedin the mode 1 state.

[0029]FIG. 19A diagrammatically illustrates an exemplary embodiment of atransceiver which supports mode 1 and mode 3 according to the invention.

[0030]FIG. 20 diagrammatically illustrates an exemplary format of aprobe packet according to the invention.

[0031]FIG. 21 illustrates in detail an example of the PLS portion ofFIG. 19.

[0032]FIG. 21A diagrammatically illustrates pertinent portions of anexemplary embodiment of the mode controller of FIG. 19A.

[0033]FIG. 21B illustrates exemplary operations which can be performedby the mode controller of FIGS. 19A and 21A.

[0034]FIG. 22 diagrammatically illustrates an exemplary format of aselection packet according to the invention.

[0035]FIG. 23 graphically illustrates exemplary PLS sampling resultsobtained according to the invention.

[0036]FIGS. 24 and 24A diagrammatically illustrate exemplary time slotformats for mode 3 communication according to the invention.

[0037]FIG. 24B illustrates exemplary operations of a retransmissiontechnique according to the invention.

[0038]FIG. 24C illustrates pertinent portions of an exemplarytransceiver embodiment that can implement operations shown in FIG. 24B.

[0039]FIG. 25 illustrates an exemplary packet format for use with thetime slot formats of FIG. 24.

[0040]FIG. 25A illustrates an exemplary ARQ packet format according tothe invention.

[0041]FIG. 26 diagrammatically illustrates an exemplary format of atraining sequence which can be used in conjunction with the packetformat of FIG. 25.

[0042]FIG. 27 illustrates a portion of the slot format of FIG. 24 inmore detail.

[0043]FIG. 28 illustrates in tabular format exemplary transmissionparameters which can be used for video transmission using mode 3according to the invention.

[0044]FIG. 29 diagrammatically illustrates exemplary acquisition andpacket reception algorithms for mode 3 operation according to theinvention.

[0045]FIG. 30 diagrammatically illustrates an exemplary embodiment of amode 3 receiver according to the invention which can implement thealgorithms of FIG. 29.

[0046]FIG. 31 diagrammatically illustrates an exemplary embodiment of amode 3 transmitter according to the invention.

[0047]FIG. 32 graphically illustrates an exemplary mapping of bits tosymbols which can be used in mode 3 operation.

[0048]FIG. 33 graphically illustrates another exemplary mapping of bitsto symbols which can be used in mode 3 operation.

[0049]FIG. 34 graphically illustrates a typical channel impulse responseencountered by transceivers according to the invention.

[0050]FIG. 35 diagrammatically illustrates an exemplary embodiment of anequalizer section which can be used to provide equalization of thechannel model of FIG. 34.

[0051]FIG. 36 diagrammatically illustrates another exemplary equalizersection which can be used to equalize the channel model of FIG. 34.

[0052]FIG. 37 diagrammatically illustrates an exemplary turbo coder foruse in conjunction with mode 3 operation according to the invention.

[0053] FIGS. 38-44 graphically illustrate exemplary simulation resultsfor mode 3 operation in various communication channels.

DETAILED DESCRIPTION

[0054] The invention includes a PHY layer solution to the IEEE 802.15Task Group 3 that offers the best solution in terms of complexity vs.performance according to the criteria document of the IEEE P802.15Working Group for Wireless Personal Area Networks (WPANs),“TG3-Criteria-Definitions”, May 11, 2000, which outlines requirementsfor high rate wireless personal area network (WPAN) systems, and whichis incorporated herein by reference. The required data rates to besupported by a high rate WPAN according to the invention are specifiedin the aforementioned criteria document. The data rates for audio are128-1450 kbps, for video are from 2.5-18 Mbps and for computer graphicsare 15, 38 Mbps. Due to the wide range for the required data rates, andin order to have a cost-effective solution covering all the data rates,the invention provides for a two or three mode system in the 2.4 GHzband. The available modes include:

[0055] (1) Mode 1 is a conventional Bluetooth 1.0 system giving a datarate of 1 Mbps.

[0056] (2) Mode 2 uses the same frequency hopping (FH) pattern asBluetooth but uses a 64 QAM modulation giving a data rate of 3.9 Mbps.

[0057] (3) Mode 3 selects a good 22 MHz band in the 2.402-2.483 GHz ISMusing a probe, listen and select (PLS) technique, and transmits up to 44Mbps using direct sequence spread spectrum (DSSS).

[0058] Examples of system parameters according to the invention aresummarized in FIG. 1. Wireless transceiver devices according to theinvention can support any combination of the aforementioned operationalmodes. Examples include: devices capable of handling mode 1+mode 2 forcovering audio and Internet streaming data rates of up to 2.5 Mbps; anddevices capable of handling mode 1+mode 3 for covering DVD-High QualityGame applications of up to 38 Mbps. These exemplary configurations areshown diagrammatically in FIG. 2.

[0059] The mode 1 for the proposed system is conventional Bluetoothoperation, which is described in detail in Specification of theBluetooth System, Version 1.0A, Jul. 26, 1999, which is incorporatedherein by reference.

[0060]FIG. 3 summarizes the parameters for mode 2 and also compares itto mode 1. An exemplary symbol rate for mode 2 is 0.65 Msymbols/sec.(other rates are also available) giving a bit rate of 2.6 Mbits/sec for16 QAM (16-ary quadrature amplitude modulation) and 3.9 Mbits/sec. for64 QAM (64-ary quadrature amplitude modulation). The transmit spectrummask for mode 2 can be, for example, the same as Bluetooth, as shown inFIG. 4. For FIG. 4, the transmitter is transmitting on channel M and theadjacent channel power is measured on channel N. The FIG. 4 spectrummask can be achieved, for example, by a raised cosine filter of a =0.54and a 3 dB bandwidth of 0.65 MHz for the symbol rate of mode 2.

[0061] In one example of operation in mode 1 and mode 2, a Bluetoothmaster and slave first synchronize to each other and communicate usingmode 1 and then enter mode 2 upon negotiation. FIG. 5 shows an exemplarytransition diagram for the master and slave to enter and exit mode 2.The entry into and exit from mode 2 is negotiable between the master andslave.

[0062] An exemplary frame format structure for master to slave and slaveto master transmissions in mode 2 is similar to mode 1 and is shown inFIG. 6. In one example the preamble consists of the pattern (1+j)* {1,−1, 1, −1, 1, −1, 1 −1, 1, −1, 1, −1, 1 −1, 1, −1, 1, −1, 1, −1}, whichaids in the initial symbol timing acquisition of the receiver. Thepreamble is followed by the 64 bit Bluetooth sync. word transmittedusing quadrature phase shift keying (QPSK), implying a 32 symboltransmission in mode 2. The sync. word is followed by the 54 bitBluetooth header transmitted using QPSK, implying 27 symbols in mode 2.The farthest constellations in the 16/64 QAM are employed for thetransmission of the preamble, sync. word and header as shown in FIG. 6A.The header is followed by a payload of 1 slot or up to 5 slots, similarto Bluetooth. The maximum number of bits in the payload is thus 7120bits for 16 QAM transmission and 10680 bits for 64 QAM transmission.

[0063] The master can communicate with multiple slaves in the samepiconet, some slaves in mode 2 and others in mode 1, as shown in theexemplary WPAN of FIG. 7. The timing diagram of FIG. 8 shows an examplefor a Bluetooth SCO HV1 link (i.e., mode 1) between the master M andslaves S₁ and S₃, with slave S₂ communicating with the master in mode 2(see also FIG. 7).

[0064] A block diagram of exemplary receiver algorithms for acquisitionand packet reception in mode 2 is shown in FIG. 9, and an exemplaryreceiver block diagram for supporting mode 2 is shown in FIG. 10. InFIG. 10, the A/D converter can sample the incoming symbols at, forexample, 2 samples/symbol, implying a 1.3 MHz sampling rate. Anexemplary transmitter block diagram for supporting mode 2 is shown inFIG. 11. Several blocks can be shared between the transmitter (FIG. 11)and the receiver (FIG. 10) to reduce the overall cost of a transceiverfor mode 2. Similarly, several blocks of the mode 2 transmitter and mode2 receiver can be used also for mode 1, thereby reducing the overallcost of implementing a transceiver for combined mode 1+mode 2.

[0065] A convolutional code of rate ½, K=5 is used at 101 in the exampleof FIG. 10 to improve the packet error rate performance in the presenceof automatic repeat requests (ARQ). Whenever the CRC of a packet isdetected in error at 102, the transmitter sends the parity bits in theretransmission. The receiver combines the received data across packetsin the Viterbi decoder to improve the overall performance of thereceiver. A flow diagram of an exemplary scheme is shown in FIG. 12.

[0066] In the example of FIG. 12, the original data bits andcorresponding CRC bits are encoded (e.g., using convolutional coding) at120 to produce an encoded result that includes the original data bitsand corresponding CRC bits, plus parity bits (redundant overhead bits)generated by the encoding algorithm. After the encoding operation at120, only the original data bits and corresponding CRC bits areinitially transmitted at 121. If the CRC at the receiver does not checkcorrectly, then a retransmission is requested at 122. In response to theretransmission request, the parity bits associated with the previouslytransmitted data bits are transmitted at 123. At the receiver, thereceived parity bits are mapped into corresponding data and CRC bitsusing conventional techniques at 125. If the CRC of the data bitsproduced at 125 is correct at 124, these data bits are then passed to ahigher layer. If the CRC does not check correctly at 124, then thereceived parity bits are combined with the associated data bits plus CRCbits (earlier-received at 121) for Viterbi decoding at 126. Thereafter,at 127, if the data bits and corresponding CRC bits generated by theViterbi decoding algorithm produce a correct CRC result, then those databits are passed to a higher layer. Otherwise, the data bits that werereceived at 121 are discarded, and a retransmission of those data bitsis requested at 128.

[0067] The original data bits and corresponding CRC bits are thenretransmitted at 129 and, if the CRC checks, the data bits are passed tohigher layer. Otherwise, the retransmitted data bits plus CRC bits arecombined with the parity bits (earlier-received at 123) for Viterbidecoding at 1200. If the data bits and corresponding CRC bits generatedat 1200 by the Viterbi decoding algorithm produce a correct CRC resultat 1201, then those data bits are passed to a higher layer. Otherwise,the parity bits that were transmitted at 123 are discarded, andretransmission of the parity bits is requested at 1202. Thereafter, theoperations illustrated generally in the flow from 123 through 1202 inFIG. 12 can be repeated until the CRC for the data bits checks correctlyor until a predetermined time-out occurs.

[0068]FIG. 12A diagrammatically illustrates pertinent portions of anexemplary transceiver embodiment which can implement receiver operationsdescribed above with respect to FIG. 12. The incoming packet dataincluding, for example, the received version of the original data bitsand corresponding CRC bits, is buffered at 1204 and is also applied toCRC decoder 1205. In response to the CRC decoding operation, acontroller 1206 generates either a negative (NAK) or positive (ACK)acknowledgment in the form of an ARQ packet for transmission to theother end. If the CRC checks correctly (ACK), then the controller 1206signals buffer 1204 to pass the buffered data to a higher layer. On theother hand, if the CRC did not check correctly (NAK), then, in responseto the negative acknowledgement, the other end will transmit the paritybits, which are input to the controller 1206 and buffered at 1204. Thecontroller 1206 maps the received parity bits into corresponding dataand CRC bits. This mapping result is applied to the CRC decoder 1205and, if the CRC checks correctly, the data bits are passed to a higherlayer at 1207.

[0069] If the CRC of the mapping result does not check correctly, thenthe controller 1206 signals a Viterbi decoder 1203 to load the paritybits and data (plus CRC) bits from the buffer 1204 and perform Viterbidecoding. The resulting data (plus CRC) bits output at 1208 from theViterbi decoder 1203 are input to the CRC decoder 1205. If the CRC ofthe Viterbi-decoded data bits checks correctly, then the controller 1206directs the Viterbi decoder to pass the Viterbi-decoded data bits to ahigher layer at 1209. On the other hand, if the CRC of theViterbi-decoded data bits does not check correctly, then the controller1206 outputs another negative acknowledgment, to which the other endwill respond by retransmitting the original data (plus CRC) bits (see129 in FIG. 12), which are received and written over thepreviously-received data (plus CRC) bits in buffer 1204. If the CRC forthese newly-received data bits does not check, then the controller 1206signals for Viterbi decoding of the newly-received data (plus CRC) bitsand the previously-received parity bits (which are still in buffer1204). If this Viterbi decoding does not result in a correct CRC for thedata bits, then controller 1206 can output another NAK, in response towhich the parity bits can be re-transmitted, input to controller 1206,and written over the previous parity bits in buffer 1204.

[0070]FIG. 12B diagrammatically illustrates pertinent portions of anexemplary embodiment of a transceiver which can implement transmitteroperations illustrated in FIG. 12. In FIG. 12B an encoder 1210 (e.g. aconvolutional encoder) encodes the uncoded data, and stores the data(plus CRC) bits and corresponding parity bits in buffer 1213. A pointer1217 driven by a counter 1211 points to a selected entry 1215 in buffer1213. The data (plus CRC) bits and the parity bits of the selected entry1215 are applied to a selector 1214 that is controlled by a flip-flop1212. The data (plus CRC) bits of entry 1215 are initially selected forthe outgoing packet. If a negative acknowledgment (NAK) is received, theflip-flop 1212 toggles, thereby selecting the parity bits of entry 1215for the next outgoing packet. For all additional negativeacknowledgments that are received, the data (plus CRC) and parity bitsof entry 1215 are alternately selected at 1214 by the toggling operationof the flip-flop 1212 in response to the received negativeacknowledgements. When a positive acknowledgment (ACK) is received, theflip-flop 1212 is cleared and the counter 1211 is incremented, therebymoving the pointer to select another data entry of buffer 1213 forconnection to the selector 1214. Of course, the counter 1211 can also beincremented in response to a pre-determined time-out condition.

[0071] Exemplary simulation results shown in FIG. 13 compare thethroughput of Bluetooth (131) against mode 2 (132, 133). The simulationassumes single path independent Rayleigh fading for each hoppingfrequency. This is a good model for mode 2, for the exponential decayingchannel model as specified in the aforementioned criteria document. Thex-axis is the average E_(b)/N_(o) of the channel over all the hoppingfrequencies. For 16 QAM (132) mode 2 achieves 2.6× throughput ofBluetooth and for 64 QAM (133) mode 2 achieves 3.9× throughput ofBluetooth. Depending on the EbNo or other available channel qualityinformation, the modulation scheme that offers the highest throughputcan be chosen.

[0072]FIGS. 14, 14C and 14D illustrate exemplary system parameters formode 3. The symbol rate in these parameter examples is 11 Msymbols/sec(which is the same as in IEEE 802.11(b)), and the spreading parameter is11 Mchips/sec for these examples. FIG. 14A shows further parameterexamples with a spreading parameter of 18 Mchips/sec and a symbol rateof 18 Msymbols/sec. The transmit spectrum mask for mode 3 can be, forexample, the same as in IEEE 802.11(b), as shown in FIG. 15. At a symbolrate of 11 Msymbols/sec this spectrum mask allows a reasonable costfilter. This spectrum mask can be achieved, for example, by a raisedcosine filter of α=0.22. In one example, the master and slave can startcommunicating in mode 1. If both devices agree to switch to mode 3, theprobe, listen and select (PLS) protocol for frequency band selection isactivated. In some exemplary embodiments, this protocol allows selection(for mode 3 transmission) of the best contiguous 22 MHz band in theentire 79 MHz range. This gives frequency diversity gains. FIG. 16 showsexemplary simulation results of the packet error rate (PER) for the IEEE802.15.3 exponential channel model as specified in the aforementionedcriteria document for a delay spread of 25 ns. The simulation results(using uncoded QPSK) compare performance using PLS according to theinvention (161) to performance without PLS (162). The delay spread of 25ns gives a frequency diversity of 3 to the PLS technique over the 79 MHzISM band. This results in a performance gain for PLS of about 15 dB.

[0073] Exemplary communications between transceivers employing modes 1and 3 can include the following: begin transmission in mode 1 and usePLS to identify good 22 MHz contiguous bands; negotiate to enter mode 3;after spending time T₂ in mode 3 come back to mode 1 for time T₁; themaster can communicate with any Bluetooth devices during time T₁ in mode1; also during time T₁ and while in mode 1, PLS can be used again toidentify good 22 MHz bands; the devices again negotiate to enter mode 3,this time possibly on a different 22 MHz band (or the same band).

[0074] An example with T₁=25 ms and T₂=225 ms is shown in the statetransition diagram of FIG. 17. These choices allow transmission of 6video frames of 18 Mbps HDTV MPEG2 video every 250 ms.

[0075] A master can communicate with several devices in mode 1 whilecommunicating with other devices in mode 3, as shown in the exemplaryWPAN of FIG. 18.

[0076] An exemplary timing diagram illustrating transmission in modes 1and 3 is shown in FIG. 19. The Master and Slave communicate in Mode 3for T₂=225 msec. while the remaining 25 ms are used for communicatingwith other Slaves (e.g. for 17.5 ms) and for PLS (e.g. for 7.5 ms) todetermine the best 22 MHz transmission for the next transmission in mode3. The time used for PLS is also referred to herein as T_(PLS.)

[0077]FIG. 19A diagrammatically illustrates an exemplary embodiment of awireless communication transceiver according to the invention. Thetransceiver of FIG. 19A supports mode 1 and mode 3 operation. A modecontroller 195 produces a control signal 196 which controls transitionsbetween mode 1 operation and mode 3 operation by selecting between amode 1 transceiver (XCVR) section 197 and a mode 3 transceiver section198. The mode controller 195 communicates at 192 with the mode 1transceiver section 197, and also communicates at 193 with the mode 3transceiver section 198.

[0078] Since the Bluetooth (mode 1) transceiver 197 is capable ofhopping at the maximum rate of 3200 hops/sec (each hop is on a 1 MHzband), this rate can be used for channel sounding. This means that theduration of each slot (master-to-slave or slave-to-master) is 312.5microseconds. A pseudorandom hopping pattern is used in someembodiments. This pattern is chosen such that the entire 79 MHz range issampled at a sufficient rate (e.g. in 5 MHz steps) to identify the best22 MHz frequency band. Using this hopping pattern the master can, inmode 1 (Bluetooth), send the slave short packets, also referred toherein as probe packets, of the format shown in FIG. 20. Notice thatexemplary probe packet of FIG. 20 is the same as a Bluetooth ID packet.The slave estimates the channel quality based, for example, upon thecorrelation of the access code (e.g. the Bluetooth sync word) of thereceived probe packet. Note that a special or dedicated probe packet isnot necessarily required, because channel quality can also be estimatedbased on normal mode 1 traffic packets.

[0079] Referring to the example of FIG. 21, after 16 probe packets (eachof time duration 312.5 microseconds including turn around time), theslave will decide on the best contiguous 22 MHz band to use in mode 3,and will then send the index of the lowest frequency of that band to themaster 8 times using 8 slots (each of time duration 312.5 microseconds).This index will be a number from 1 to 57 (79 (bandwidth of ISM band)−22(bandwidth in mode 3)=57), and thus requires a maximum of 6 bits. These6 bits are repeated 3 times, so the payload of each slave-to-masterpacket (FIG. 22), also referred to herein as selection packets, will bea total of 18 bits. This leaves 226 μsec. for the turn around time. Thenumber n (e.g. 16 in FIG. 21) of master-to-slave packets and the numberk (e.g. 8 in FIG. 21) of slave-to-master packets can be predefined bythe PLS protocol or agreed upon during the initial handshake between themaster and slave. Also, the slave can send probe packets to the masterso the master can evaluate the slave-to-master channel.

[0080] The channel state of each 1 MHz band can be estimated, forexample, by using the maximum value of the correlation of the accesscode or any known part of the probe packet. This gives a good estimateof the amplitude of the fading parameter in that 1 MHz channel. The best22 MHz band can then be chosen using this information.

[0081] For example, for each contiguous 22 MHz frequency band, where thejth frequency band is designated f(j), a quality parameter q_(f(j)) canbe calculated as follows$q_{f{(j)}} = {\sum\limits_{i}\left| \alpha_{i} \right|^{2}}$

[0082] where |α_(i)| is the magnitude of the fading parameter amplitudeestimate (e.g. a correlation value) for the ith frequency hop in f(j).The frequency band f(j) having the maximum q_(f(j)) is taken to be thebest band.

[0083] As another example, a quality parameter q_(f(j)) can becalculated for each contiguous 22 MHz band as

q_(f(j))=min |α_(i|)

[0084] and the band f(j) having the maximum q_(f(j)) is selected as thebest band.

[0085] As another example, the following quality parameters can becalculated for each contiguous 22 MHz band:$q_{f{(j)}} = {\sum\limits_{i}\left| \alpha_{i} \right|^{2}}$

 A_(f(i))=min|α_(i|)

B_(f(j))=max |α_(i|)

[0086] Those frequency bands f(j) whose associated A_(f(j)) and B_(f(j))produce a ratio A_(f(j))/B_(f(j)) larger than a predetermined thresholdvalue can be identified, and the one of the identified frequency bandshaving the largest q_(f(j)) is taken to be the best band. The thresholdvalue can be determined, for example, empirically on the basis ofexperimentation for desired performance in expected channel conditions.

[0087] Consider a PLS example with n=16 and k=8. This indicates that the79 MHz band should be sampled in 5 MHz steps. The hopping pattern istherefore given by:

[0088] o={0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75}.

[0089] The ith PLS frequency hop is defined to be f(i)=(x+o(i))mod(79);i=1, 2 . . . , 16

[0090] Here x is the index of the Bluetooth hopping frequency that wouldoccur at the beginning of the PLS procedure, and can have values of x=0,1, 2, . . . , 78. The index i can be taken sequentially from a pseudorandom sequence such as:

[0091] P={16, 4, 10, 8, 14, 12, 6, 1, 13, 7, 9, 11, 15, 5, 2, 3}.

[0092] Different pseudo random sequences can be defined for differentvalues of n and k.

[0093] The 8 transmissions from the slave to the master can use, forexample, the first 8 frequencies of the sequence f(i), namely f(i) fori=1, 2, . . . , 8.

[0094] The above exemplary procedure can be summarized as follows:

[0095] 1. Master sends to the slave the probe packet on the frequenciesdetermined by the sequence f(i). The transmit frequency is given by(2402+f(i)) MHz;

[0096] 2. Slave estimates the quality of each channel;

[0097] 3. After 16 master-to-slave probe packets, the slave estimatesthe best 22 MHz band using all the quality information it hasaccumulated;

[0098] 4. The slave sends to the master a selection packet including theindex of the lowest frequency of the best 22 MHz band;

[0099] 5. The slave repeats step 4 a total of 8 times; and

[0100] 6. Transmission starts in mode 3 using the selected 22 MHz band.

[0101] Example results of the PLS procedure applied to the exponentiallyfading IEEE 802.15.3 channel for a delay spread of 25 ns. are shown inFIG. 23 wherein the 79 MHz channel is sampled at a 5 MHz spacing. Asshown, the 5 MHz spacing can identify good 22 MHz contiguous bands inthe 79 MHz bandwidth. The 1, 5, 22 and 79 MHz parameters described aboveare of course only exemplary; other values can be used as desired. Asone example, rather than hopping on 1 MHz channels, the system could hopover different bandwidth channels (e.g. a 22 MHz channel) and transmitdata occupying the whole channel.

[0102]FIG. 21A diagrammatically illustrates pertinent portions of anexemplary embodiment of the mode controller of FIG. 19A. The embodimentof FIG. 21A includes a probe and selection controller 211 which outputsto the mode 1 transceiver section 197 information indicative of thefrequencies on which the probe and selection packets are to betransmitted, and can also provide the probe and selection packets to themode 1 transceiver section 197, depending upon whether the probe portionor the select portion of the above-described PLS operation is beingperformed. A band quality determiner 212 receives conventionallyavailable correlation values from the mode 1 transceiver section 197 anddetermines therefrom band quality information which is provided at 215to a band selector 213. The band quality information 215 can include,for example, any of the above-described quality parameters. The bandselector 213 is operable in response to the quality information 215 toselect the preferred frequency band for mode 3 communications. Forexample, the band selector 213 can use any of the above-described bandselection criteria. The band selector 213 outputs at 216 to the probeand selection controller 211 the index of the lowest frequency of thepreferred frequency band. The probe and selection controller 211includes the received index in the selection packets that it provides tothe mode 1 transceiver section 197 for transmission to the othertransceiver involved in the PLS operation.

[0103] The mode controller of FIG. 21A also includes a frequency bandmapper 214 which receives selection packets from the other transceiverinvolved in the PLS operation. The frequency band mapper extracts theindex from the selection packets and determines therefrom the selected22 MHz frequency band. Information indicative of the selected frequencyband is output from the frequency band mapper 214 to the mode 3transceiver section 198, after which mode 3 communication can begin.

[0104]FIG. 21B illustrates exemplary operations which can be performedby the transceiver of FIGS. 19A and 21A. At 221, the aforementionedparameters n, k, T₁, T₂ and T_(PLS) are determined, for example, duringinitial handshaking. At 222, the transceiver operates in mode 1 for aperiod of time equal to T₁-T_(PLS). Thereafter, at 223, n probefrequencies within the available bandwidth (BW) are determined, and aprobe packet is transmitted on each probe frequency at 224. At 225, theprobe packets are received and corresponding frequency channel qualityinformation (for example maximum correlation values) is obtained. At226, the frequency channel quality information is used to produce bandquality information, and the band quality information is used at 227 toselect a preferred frequency band for mode 3 communication. At 228, kselection packets are transmitted on k different frequencies, eachselection packet indicative of the selected frequency band. At 229, mode3 communications are performed using the selected frequency band for atime period of T₂. After expiration of the time T₂, mode 1communications resume at 222, and the above described operations arerepeated.

[0105]FIG. 14B diagrammatically illustrates pertinent portions of afurther exemplary embodiment of the mode controller of FIG. 19A. In theFIG. 14B embodiment, a modulation and coding mapper 141 receives at 142from the band selector 213 (See FIG. 21A) the band quality informationassociated with the 22 MHz band selected during the PLS procedure. Themodulation and coding mapper 141 maps the band quality information onto,for example, any of the exemplary modulation and channel codingcombinations shown at 1-22 in FIGS. 14, 14A, 14C and 14D. At 143, themapper 141 provides to the mode 3 transceiver section 198 informationindicative of the selected modulation and channel coding combination.The mapping operation can be defined, for example, so as to maximize thesystem throughput given the band quality information of the selectedband. In some exemplary embodiments, experimental simulation informationsimilar to that shown in FIG. 13 above, for example, throughput versusband quality for different modulation schemes and also for differentcoding rates, can be used by the mapper 141 to select the combination ofmodulation scheme and coding rate that provides the highest throughput,given the band quality of the selected band.

[0106] Referring again to FIGS. 17 and 19, several packets can betransmitted from the master to the slave and vice versa in the time slotperiod T₂ (e.g. 225 ms) allocated for mode 3. A nominal packet size of,for example, 200 microseconds can be used, as shown in FIG. 24. Duringtheir initial handshake, the master and the slave can, for example,agree on a certain number of packets to be sent in each direction. Theycan also agree (during the handshake) on the modulation scheme to beused in each direction.

[0107] In an example of one-way communications, and if ARQ (automaticrepeat request) is used, the transmitting device can, for example, senda predetermined number of normal packets (also referred to herein as asuperpacket). The number of normal packets in the superpacket can beagreed upon in initial handshaking. After receipt of the predeterminednumber of normal packets, the receiving device can, for example, send ashort ARQ packet that is half the length of a normal packet. The ARQpacket can be preceded and followed by guard intervals (e.g. 100microseconds). The ARQ packet serves to acknowledge the reception of thenormal packets. Those packets whose CRC (cyclic redundancy code) did notcheck correctly are indicated in the ARQ packet. The transmitter canthen send the requested packets again in a further superpacket. Thisprocedure can be repeated until all packets get through or a time-outoccurs. FIG. 24 shows an exemplary slot format for the case of one-waycommunication, either from master to slave (explicitly shown) or slaveto master (not explicitly shown), with and without ARQ.

[0108] Two-way mode 3 communication from master to slave and slave tomaster can be handled similarly, as illustrated in the example of FIG.24A.

[0109] ARQ and retransmissions are optional. Retransmissions canincrease the mode 3 performance in the presence of an interferer (suchas a Bluetooth device). Referring to FIG. 24 for one-way transmissionwith ARQ, an exemplary retransmission technique (illustrated in FIG.24B) is as follows:

[0110] 1. The master sends the slave a superpacket at 2401 including 100packets with CRC at the end of each packet.

[0111] 2. The slave uses the CRC at 2402 to determine if the packetswere received without error.

[0112] 3. The slave sends the master an ARQ packet that has a payload of100 bits (see 2430, 2431 in FIG. 24B). Each bit corresponds to areceived packet. The bit is 1 if the packet was received with no error,and is zero if it was received in error. A CRC is appended at the end ofthe ARQ packet.

[0113] 4. If the master receives the ARQ packet correctly at 2404, themaster retransmits the requested packets (if any) to the slave (see 2405in FIG. 24B). If the master does not receive the ARQ packet correctly at2404 (as indicated, for example, by a failed CRC check), then

[0114] (a) the master sends the slave an ARQ packet of size 100 μsec.(see 2410 in FIG. 24B) asking for the slave's ARQ packet.

[0115] (b) the master then listens at 2404 for the slave's ARQ packet.

[0116] (c) Steps (a) and (b) are repeated by the master until hereceives at 2404 the slave's ARQ packet (sent at 2420 in FIG. 24B) andretransmits the requested packets, if any (see 2408), at 2405, or untilthe T₂ time slot ends at 2406, at which time mode 1 communicationsbegin.

[0117] 5. Steps 2-4 are repeated until all the packets are received bythe slave correctly (see 2408) or the T₂ time slot ends.

[0118] 6. If the T₂ time slot does not end during step 4 or step 5 (see2409), the master sends new packets to the slave.

[0119] If the master finishes sending all its packets before the T₂ timeslot ends, it can go to mode 1 and communicate with other Bluetoothdevices. For example, if MPEG 2 of rate 18 Mbps is being transmitted,six frames (250 ms of video) would require 204.5 ms at the rate of 22Mbps. If T₁+T₂=250 ms, and 10 ms are used for retransmission requestsand retransmissions, and if 7.5 ms is used for PLS, this would leave themaster 28 ms for mode 1 Bluetooth communications.

[0120] Retransmissions for two-way communications (See FIG. 24A) can beaccomplished similarly to the above-described one-way communications.The slave device's ARQ requests maybe piggybacked onto the slave datapackets, or independent ARQ packets can be utilized.

[0121]FIG. 24C diagrammatically illustrates pertinent portions ofexemplary embodiments of a mode 3 transceiver capable of implementingthe exemplary retransmission technique described above and illustratedin FIG. 24B. In FIG. 24C, the incoming superpacket data is applied to aCRC decoder 242 which performs a CRC check for each packet of thesuperpacket. For a given packet, the CRC decoder 242 can shift a bitinto the register 243, for example a bit value of 1 if the CRC for thepacket checked correctly, and a bit value of 0 if the CRC for the packetdid not check correctly. Thus, the register 243 will be loaded with abit value for each packet of the superpacket. The bit values containedin the register 243 are input to logic 244 which determines whether ornot the CRC of every received packet checked correctly. If so, the logicoutput 248 signals a buffer 241, into which the incoming superpacketdata has been loaded, that the superpacket data can be passed on to ahigher layer. On the other hand, if the logic 244 determines that theCRC of one or more of the received packets did not check correctly, thenthe logic output 248 signals the buffer 241 to hold the superpacketdata.

[0122] The contents of register 243 are also provided to an ARQgenerator 245 which uses the register contents to fill the payload of anoutgoing ARQ packet. When a superpacket including retransmitted packetsis received, the retransmitted packets are buffered into theirappropriate superpacket locations in buffer 241, and the CRC decoder 242performs a CRC check for each retransmitted packet, providing the CRCresults to the register 243.

[0123] An ARQ receiver 246 receives incoming ARQ packets and respondsthereto either by prompting the ARQ generator 245 to send an appropriateARQ packet, or by selecting requested packets of a previously buffered(see 247) outgoing superpacket for retransmission to the other side.

[0124] Point-to-multipoint communications can be achieved by timedivision multiplexing between various slaves. Each time slot for eachslave can be preceded by a PLS slot between the master and the concernedslave.

[0125] In some embodiments, each 200 μsec. length packet in FIG. 24includes data bits (payload) and a CRC of length 32 bits. The CRC is a32-bit sequence generated, for example, using the following polynomialD³²+D²⁶+D²³+D²²+D¹⁶+D¹²+D^(11+D) ¹⁰+D⁸+D⁷+D⁵+D⁴+D²⁺¹. This exemplarypacket format is shown in FIG. 25.

[0126]FIG. 25A illustrates an exemplary ARQ packet format according tothe invention. The ARQ packet format of FIG. 25A is generally similar tothe packet format shown in FIG. 25, and includes the training sequenceof FIG. 26. The payload of the FIG. 25A packet is protected by arepetition code. The size of the FIG. 25A packet can be specified in itsheader, or can be determined by the master based on: the number ofpackets in the superpacket sent by the master multiplied by therepetition code rate; the number of CRC bits; and the number of trainingbits.

[0127] Several of the packets in FIG. 24, the number of which can beagreed upon in the initial handshake, are preceded by a trainingsequence for acquisition of timing, automatic gain control and packettiming. Typically 10 packets are preceded by the training sequence. FIG.26 shows an exemplary format of the training sequence. FIG. 27illustrates diagrammatically a portion of the above-described exemplaryslot format of period T₂ in mode 3, including the training sequence (seealso FIG. 26) and the CRC.

[0128] The preamble of the FIG. 26 training sequence includes thepattern (1+j)* 1, −1, 1, −1, 1, −1, 1, −1, 1, −1, 1, −1, 1, −1, 1, −1,1, −1, 1, −1 ] and it aids in the initial symbol timing acquisition bythe receiver. The preamble is followed in this FIG. 26 example by the64-bit Bluetooth sync. word transmitted using quadrature phase shiftkeying (QPSK), implying a 32 symbol transmission in mode 3. The sync.word is followed by the header transmitted using QPSK modulation. Thefarthest constellations in the 16 QAM are employed for the transmissionof the preamble, sync. word and header (see FIG. 6). Referring also toFIG. 27, the header is followed by a payload such that the total timeoccupied by the packet is 200 microseconds. The payload is followed bythe 32-bit CRC.

[0129] It should be understood that the above-described slot and packetformats are exemplary only and that, for example: the packet length canbe set to any desired length; a different size polynomial can be usedfor the CRC; and a different size training sequence can be used with thepreamble, sync word and header sized as desired. It should also beunderstood that the above-described slot and packet formats are readilyapplicable to two-way communications.

[0130] The exemplary slot and packet formats described above permit, forexample, transmission of HDTV MPEG2 video at 18 Mbps. Assume, forexample, that 24 frames/sec. is transmitted for MPEG 2 video. Thus, themaster transmits to the slave 100 packets each of length 200 μsec.carrying a data payload of 2184 symbols. Assuming, for example, that 10such packets are preceded by the training sequence of 81 symbols (FIG.26), and that 16 QAM with rate ½ coding is used, 206.8 msec. is neededfor transmission of 6 video frames. Assuming a 9% ARQ rate implies thatthe total time required for 6 video frames is 225 msec. FIG. 28summarizes exemplary transmission parameters for HDTV MPEG2 videotransmission using mode 3.

[0131] The receiver algorithms for acquisition and packet reception inmode 3 are similar to mode 2. An exemplary block diagram of mode 3receiver algorithms is shown in FIG. 29. An exemplary receiverembodiment for mode 3 is shown diagrammatically in FIG. 30. Thedemodulator of FIG. 30 shown generally at 301 can include, for example,channel estimation, equalization, and symbol-to-bit mapping.

[0132] An exemplary transmitter embodiment for mode 3 is shown in FIG.31. Each D/A converter 310 on the I and Q channels can be, for example,an 6-bit 44 MHz converter. The transmitter and receiver of FIGS. 31 and30 can be used together to form the exemplary mode 3 transceiver of FIG.19A above.

[0133] In some exemplary embodiments, modulation options such as QPSK,16-QAM and 8-PSK (8-ary phase shit keying) can be used in mode 3, asshown in FIGS. 32, 32A and 33. Referring to the QPSK example of FIG. 32,an exemplary cover sequence S, such as used in IEEE 802.11, is used tospread the transmitted symbols. The mapping from bits to symbols isshown in FIG. 32. Referring to the 8-PSK example of FIG. 32A, the coversequence S, as used in IEEE 802.11, is used to spread the transmittedsymbols. The mapping from bits to symbols is shown in FIG. 32A.Referring to the 16-QAM example of FIG. 33, the cover sequence (alsoreferred to herein as a scrambling code) S, as used in IEEE 802.11, isused to spread the transmitted symbols. The mapping from bits to symbolsis shown in FIG. 33. In the examples of FIGS. 32 and 33, S_(i)represents the ith member of the sequence S, and is either 1 or 0. Insome embodiments, no cover sequence is used, in which case theconstellations associated with either value of S can be used.

[0134] The exponentially delayed Rayleigh channel example shown in FIG.34 is typical of an anticipated operating environment and may thereforebe used to test performance. The complex amplitudes of the channelimpulse response of FIG. 34 are given byh_(i) = N(0, σ_(k)²/2) + j  N(0, σ_(k)²/2)σ_(k)² = σ₀²^(−kT_(s)/T_(RMS)) σ₀² = 1 − ^(−T_(s)/T_(RMS))T_(RMS) = 25

[0135] This channel model requires equalization (at the outputs of thefilters 305 in FIG. 30), and this can be done in a variety of ways, twoconventional examples of which are described below with respect to FIGS.35 and 36.

[0136] A block diagram of an exemplary MMSE (minimum mean squared error)equalizer section is shown in FIG. 35. The equalizer section includes anMMSE equalizer, followed by a block DFE (decision feedback equalizer).The MMSE produces at 350 decisions on all the symbols using the minimummean squared error criterion and an estimate of the channel. The DFEsubtracts the decisions of all the symbols obtained by the MMSE from theinput signal and then produces at 351 matched filter soft-decisions onall the symbols. These are then fed to a soft-decisions block thatproduces at 352 soft decisions on the bit-level. These bit-level softdecisions are in turn fed to the turbo-decoder 307 (see FIG. 30) or to athreshold device in the case of an uncoded system.

[0137] The exemplary MAP equalizer section of FIG. 36 maximizes the aposteriori probabilities of the transmitted symbols given the receivedsignal and an estimate of the channel. These symbol probabilities 360are then converted to bit probabilities by summing over the symbols at361. These bit probabilities 362 are then input to the turbo decoder ora threshold device.

[0138] Video transmission typically requires a BER of 10⁻⁸, so turbocoding is used to achieve this error rate. Parallel concatenatedconvolutional codes (PCCC) are known to have an error floor at about10⁻⁷, while serial concatenated convolutional codes (SCCC) do not havean error floor and can meet the BER requirements. The SCCC in FIG. 37 isconventional, and was originally proposed by Divsalar and Pollara in“Serial and Hybrid Concatenated Codes with Applications,” ProceedingsInternational Symposium of Turbo Codes and Applications, Brest, France,September 1997, pp. 80-87, incorporated herein by reference.

[0139] Exemplary results of Monte-Carlo simulations for mode 3 are givenin FIGS. 38-44. In all simulations a frame size with 4096 informationbits was used. FIGS. 38 and 39 show the FER and BER in an AWGN channel.FIGS. 40 and 41 show the FER and BER in the IEEE 802.15.3 multipathchannel without fading. FIGS. 42 and 43 show the FER and BER in the IEEE802.15.3 multipath channel with fading. FIG. 44 shows the FER in asingle-path Rayleigh fading channel.

[0140] Due to typical transceiver size constraints, a single antenna maybe desirable for transmit and receive according to the invention.However, it is possible to use two antennas for transmit and receivediversity. Simple schemes like switched diversity can be easilyincorporated in a given transceiver device according to the invention,while also being transparent to other devices (e.g. in a Bluetoothpiconet). The modulation techniques described above are also applicableto more complex transmit diversity techniques such as, space timecoding, beam forming and others.

[0141] The aforementioned modulation schemes of the invention also allowmore complex coding schemes like parallel concatenated trellis codedmodulation (PCTCM) and serially concatenated trellis coded modulation(SCTCM). Also, a lower complexity trellis code (which can perform betterthan the turbo coding of FIG. 37) can easily be incorporated intransceiver devices according to the invention.

[0142] As discussed above, FIGS. 10 (receiver) and 11 (transmitter)illustrate an exemplary transceiver for mode 2. Many parts of the mode 2receiver, for example, the front end filter 105, LNA 106, RF/IFconverter 107, and the SAW filter 108 can be shared with mode 1. Thebaseband for a mode 2 receiver requires additional logic (beyond mode 1)for receive filtering, AGC, timing acquisition, channel estimation, QAMdemodulation and Viterbi decoding in the case of ARQ. In someembodiments, the extra gate count for this additional logic isapproximately 10,000 gates.

[0143] As discussed above, FIGS. 30 (receiver) and 31 (transmitter)illustrate an exemplary transceiver for mode 3. Many parts of the mode 3receiver, for example, the front end filter 308, LNA 306, and RF/IFconverter 302 can be shared with mode 1. The implementation of mode1+mode 3 will require an additional SAW filter over a mode 1implementation because of the larger bandwidth of mode 3 compared tomode 1. The baseband for a mode 3 receiver requires additional logic(beyond mode 1) for AGC, timing acquisition, channel estimation, QAMdemodulation, equalization and turbo decoding. In some embodiments, theextra gate count for this additional logic is approximately 100,000gates.

[0144] It will be evident to workers in the art that exemplarytransceiver embodiments according to the invention can be realized, forexample, by making suitable hardware and/or software modifications in aconventional Bluetooth MAC. Some exemplary advantages provided by theinvention as described above are listed below.

[0145] Interoperability with Bluetooth: a high rate WPAN piconetaccording to the invention can accommodate several mode 1 (Bluetooth)and mode 2 or mode 3 devices simultaneously.

[0146] High Throughput: in mode 3 a high rate WPAN according to theinvention supports 6 simultaneous connections each with a data rate of20 Mbps giving a total throughput of 6×20=120 Mbps over the whole 2.4GHz ISM band. In mode 2 the high rate WPAN supports the same number ofconnections as Bluetooth with a data rate of up to 4 Mbps each.

[0147] Coexistence: there is only a 10% reduction in throughput forBluetooth in the vicinity of an exemplary WPAN according to theinvention. The PLS technique implies a 0% reduction in throughput forIEEE 802.11 in the vicinity of a WPAN according to the invention becausePLS will select a different frequency band.

[0148] Jamming Resistance: the PLS technique helps avoid interferencefrom microwave, Bluetooth and IEEE 802.11, thus making it robust tojamming.

[0149] Low Sensitivity Level: exemplary sensitivity level for mode 2 is−78 dBm and for mode 3 is −69 dBm.

[0150] Low Power Consumption: the estimated power consumption for mode 2in year 2001 is 25 mW average for receive and 15 mW average fortransmit, and the estimated power consumption for mode 3 in year 2001 is95 mW average for receive and 60 mW average for transmit.

[0151] Although exemplary embodiments of the invention are describedabove in detail, this does not limit the scope of the invention, whichcan be practiced in a variety of embodiments.

What is claimed is:
 1. A method of communicating data from atransmitting end to a receiving end, comprising: the transmitting endapplying to a plurality of original data bits that are to be transmittedto the receiving end an encoding algorithm that produces overhead bits;the transmitting end transmitting the original data bits without theoverhead bits in a first transmission to the receiving end; and thetransmitting end refraining from transmitting the overhead bits untilthe transmitting end receives an indication from the receiving end thatthe original data bits have not been correctly received at the receivingend.
 2. The method of claim 1, including the transmitting endtransmitting the overhead bits to the receiving end in a secondtransmission in response to an indication from the receiving end thatthe original data bits have not been correctly received at the receivingend.
 3. The method of claim 2, including the receiving end combining areceived version of the original data bits and a received version of theoverhead bits to produce a combined set of received bits, and thereceiving end applying to the combined set of received bits a decodingalgorithm that corresponds to said encoding algorithm.
 4. The method ofclaim 2, including the receiving end applying to a received version ofthe overhead bits a mapping operation which, if the overhead bits havebeen received correctly at the receiving end, will result in theoriginal data bits, and the receiving end applying an error detectionprocedure to the result of the mapping operation to determine whetherthe mapping operation has resulted in the original data bits and, inresponse to a determination that the mapping operation has not resultedin the original data bits, the receiving end combining the receivedversion of the overhead bits with a received version of the originaldata bits to produce a combined set of received bits, and the receivingend applying to the combined set of received bits a decoding algorithmthat corresponds to said encoding algorithm.
 5. The method of claim 4,wherein said encoding and decoding algorithms are Viterbi encoding anddecoding algorithms.
 6. The method of claim 4, including the receivingend applying an error detection procedure to a result of said decodingalgorithm to determine whether said decoding algorithm has resulted inthe original data bits and, in response to a determination that saiddecoding algorithm has not resulted in the original data bits, thereceiving end transmitting to the transmitting end a request forretransmission of the original data bits.
 7. The method of claim 6,including the transmitting end retransmitting the original data bits tothe receiving end and, in response to a determination by the receivingend that said retransmission of the original data bits has not beenreceived correctly, the receiving end combining a received version ofthe retransmitted original data bits with said received version of theoverhead bits to produce another combined set of received bits, and thereceiving end applying said decoding algorithm to said another combinedset of received bits.
 8. A method of communicating data from atransmitting end to a receiving end, comprising: the receiving endreceiving from the transmitting end a first transmission includingoriginal data bits; the receiving end determining whether the originaldata bits have been received correctly and, responsive to adetermination that the original data bits have not been receivedcorrectly, the receiving end transmitting to the transmitting end arequest for transmission of overhead bits produced at the transmittingend by operation of an encoding algorithm applied to the original databits.
 9. The method of claim 8, wherein the encoding algorithm is aconvolutional encoding algorithm.
 10. A data communication apparatus,comprising: an input for receiving original data bits that are to betransmitted via a communication channel to another data communicationapparatus; an encoder coupled to said input for applying to the originaldata bits an encoding algorithm that produces overhead bits; an outputfor providing bits that are to be transmitted across the communicationchannel; and a data path coupled between said encoder and said outputfor selectively providing to said output one of the original data bitsand the overhead bits, said data path having a control input forreceiving control information from said another communication apparatus,said data path responsive to said control information for selecting oneof the original data bits and the overhead bits to be provided to saidoutput for transmission across the communication channel to said anotherdata communication apparatus.
 11. The apparatus of claim 10, whereinsaid data path includes a buffer coupled to said encoder for storing theoriginal data bits and the overhead bits.
 12. The apparatus of claim 11,wherein said data path includes a selector coupled between said bufferand said output, said selector responsive to said control input forobtaining one of the original data bits and the overhead bits from saidbuffer to be provided to said output for transmission to said anotherdata communication apparatus.
 13. The apparatus of claim 10, whereinsaid control information includes a negative acknowledgement indicatingthat an earlier transmission has not been received correctly at saidanother communication apparatus, said data path responsive to thenegative acknowledgement for changing its selection from one of theoriginal data bits and the overhead bits to the other of the originaldata bits and the overhead bits.
 14. The apparatus of claim 10, providedas a wireless communication apparatus.
 15. The apparatus of claim 10,wherein said encoder is a convolutional encoder.
 16. A datacommunication apparatus, comprising: an input for receiving a receivedversion of original bits transmitted over a communication channel byanother data communication apparatus; an error detector coupled to saidinput for determining whether the received version of the original databits is correct; and a controller coupled to said error detector andresponsive to a determination that the received version of the originaldata bits is incorrect for providing for transmission to said anotherdata communication apparatus a request for said another datacommunication apparatus to transmit overhead bits produced at saidanother data communication apparatus by operation of an encodingalgorithm applied to the original bits.
 17. The apparatus of claim 16,wherein said input is further for receiving a received version of theoverhead bits as transmitted from said another data communicationapparatus, said controller coupled to said input for applying to thereceived version of the overhead bits a mapping operation which, if theoverhead bits have been received correctly at the receiving end, willresult in the original data bits, said error detector coupled to saidcontroller for applying an error detection procedure to the result ofthe mapping operation to determine whether the mapping operation hasresulted in the original data bits.
 18. The apparatus of claim 17,including a decoder coupled to said input and said controller, saidcontroller responsive to a determination by said error detector that themapping operation has not resulted in the original data bits forsignaling said decoder to apply to the received version of the originaldata bits and the received version of the overhead bits a decodingalgorithm that corresponds to said encoding algorithm.
 19. The apparatusof claim 18, including a buffer coupled between said input and saiddecoder for storing the received version of the original bits and thereceived version of the overhead bits for use by said decoder.
 20. Theapparatus of claim 18, wherein said error detector is coupled to saiddecoder for determining whether said decoding algorithm has resulted inthe original data bits, said controller operable in response to adetermination that said decoding algorithm has not resulted in theoriginal data bits for providing for transmission to said another datacommunication apparatus a request for retransmission of the originaldata bits.
 21. The apparatus of claim 18, wherein said decoder is aViterbi decoder.
 22. The apparatus of claim 16, provided as a wirelesscommunication apparatus.